1. Field of the Invention
The present invention concerns transmission devices designed to be placed between a first member, hereinafter referred to as the driving member, and a second member, hereinafter referred to as the driven member, and is more particularly, but not exclusively, concerned with the situation in which the driven member constitutes or is associated with a vibrating machining tool.
2. Description of the Prior Art
As is well known, it is common practice to subject tools to subsonic or ultrasonic mechanical vibration in order to increase productivity.
For the tool, constituting the driven member, to be subjected to vibration by a vibration generator, constituting the driving member, in practice a transducer itself connected to a pulse generator, a transmission device must be disposed between the tool and the bed of the machine to which it is fitted. This is to attach the tool to and to correctly position it relative to the bed, which constitutes a reference support, and also to enable the tool to be acted upon by the vibration generator.
The general problem to be overcome in the design of such transmission devices is that they must transmit vibration without attenuating it from the vibration generator constituting the driving member to the tool constituting the driven member, without transmitting the vibration to the bed of the machine forming the reference support (in order to protect other units mounted on same) and in such a way, in at least certain applications (spark erosion machines, for example), as to provide electrical insulation between the tool (in this instance a working electrode) and the bed.
Transmission devices so far proposed for this purpose comprise, for example, dampers of an elastic material, elastic diaphragms and hydrodynamic and aerodynamic suspension techniques.
At least some of these devices comprise a hollow casing to be attached to the bed forming the reference support and a core member disposed in the casing and free to move therein in all directions, the core member having at least two arms extending to the outside of the casing and to each of which either the driving member or the driven member may be connected.
However, in embodiments of this type disclosed to date the two arms of the "floating" core member are always in practice aligned with one another.
This has a number of disadvantages.
Firstly, it provides only for linear transmission of vibration from the driving member to the driven member, so that the overall assembly is relatively bulky.
The driving member and the driven member are necessarily disposed between the head of the machine supporting the assembly and the working table of the bed on which the workpiece is placed.
To secure good vibration propagation conditions the driving member and the driven member are necessarily of a length at least equal to the half-wavelength of the vibration, generally a significant length.
Also, the power input is limited to the power output of the single driving member which may be used.
Also, in certain cases at least, the positioning of the tool forming the driven member is insufficiently accurate.
Finally, it is difficult to attach the assembly to the head of the machine in such a way as to conform to the required conditions of electrical insulation, in particular through the location of the vibration generator constituting the driving member between the casing and the head.
This is the primary reason for which, in spark erosion machine tools known as of this date and using a vibrating tool, it is necessary in practice to alternate the application of voltage to the tool with the application of vibration to it. This prevents the full benefit of applying vibration to the tool being obtained.
One object of the present invention is to provide a transmission device using a fluid suspension which overcomes these disadvantages and offers additional advantages. Another object of the invention is to provide a machine tool incorporating the aforementioned transmission device.